1. Field of the Invention
The present invention relates to a signal transmission apparatus of a DC brushless motor. More particularly, the present invention relates to a signal transmission apparatus used in a DC brushless motor of a ceiling fan for transmitting at least one processed output signal from at least one sensor, wherein the output signal represents a variation of the magnetic pole operations in the DC brushless motor.
2. Descriptions of the Related Art
DC brushless motors have several advantages, such as a high torque at low speeds and low electromagnetic interference. In addition, they are free of noise and carbon brush maintenance. However, to successfully start and maintain smooth operation of a DC brushless motor from its stationary state, the sensors (e.g., Hall sensor) have to be mounted in the motor to sense the variation of the magnetic fields from the rotation of the magnets. The motor control signal can then be generated to ensure continuous and steady operation of the motor.
For example, in a three-phase DC brushless motor, three sensors and a permanent magnet are required. FIG. 1 illustrates a circuit block diagram of a DC brushless motor 2 and a controller 3 in a ceiling fan (not shown). The DC brushless motor 2 comprises a magnet 21 with two magnetic poles 211 and 212, three excitation coils 22, 23 and 24, and three sensors 25, 26 and 27. The controller 3 is connected to the excitation coils 22, 23 and 24, respectively, through the coil-energizing lines 31, 32 and 33, to control the operation of the DC brushless motor 2. It can be seen from FIG. 1 that at least five transmission lines are needed between the motor and the controller to (1) transmit the three sensing signals 251, 261 and 271 through the respective lines, (2) power the sensor through the transmission line 28 and (3) supply a reference voltage level through the reference voltage level line 29. FIG. 2 illustrates a schematic view of the connection between the DC brushless motor 2 and a controller 3 in a ceiling fan 1, in which the sensors (only one sensor 25 is illustrated here as an example) are located outside of the DC brushless motor 2. The sensing signals are transmitted to the controller 3 via five transmission lines.
Drilling is required to route the transmission lines between the motor and the controller. However, this is an invasive process that often ends in hardware damage. For example, to mount the three-phase DC brushless motor to the ceiling fan, large connecting holes have to be drilled into the motor axis so that the transmission lines can pass therethrough and connect to the controller. These large connecting holes may degrade the durability of the motor axis, and consequently, place the user at risk for injury after a long period of service.